DE1261033B - Process for the continuous covering of film webs made of cellulose hydrate - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

B44d

German KL: 75 c -5/06

Number:
File number:
Registration date:
Display day:

P 23628 VI b / 75 c
October 2, 1959
February 8, 1968

The invention relates to a method for continuous Coating of film webs made of cellulose hydrate with aqueous dispersions of polymers, in particular vinylidene chloride copolymers, in which the coated surfaces with opposite directions to Direction of travel of the web moving smoothing rollers arranged on each side of the web come into contact.

Continuous coating of the surface of endless sheets of film has been around for a number of years Done with success by first passing the slide through an immersion tank containing a liquid coating agent contains, then by a doctor device, which the remaining on the web surfaces Controls the amount of coating agent, then to smoothen and improve the quality of the coating through a smoothing device with a number of pairs of rollers and finally through a heated one Drying zone directs (VDI magazine, 1958, p. 547). With the advancement of polymeric coatings, e.g. B. those of vinylidene chloride copolymers applied from aqueous dispersions of the polymer however, are coating defects known as banding (i.e., tiny grooves or channels in the coating, which appear as a series of essentially parallel lines) occurred, due to an interaction (1) of the high solids content aqueous Dispersion coating baths and (2) rapidly imbibing the aqueous dispersant into the hydrophilic Web material that accelerates drainage and, consequently, the hardening of the coating. Until now Aids used to smooth the coating before it solidifies (hardening) turn out to be in the generally considered insufficient and in terms of eliminating streaking in coatings that result from aqueous dispersions are applied to hydrophilic bases, as generally unsatisfactory. The reason for this is that it occurs in the very short period of time between the metered application the coating on the base material and the point in time at which the coating becomes too hard, to respond to the effect of the smoothing devices are not working effectively, or by the smoothing devices If the inhibition resistance is too strong, this leads to markings on the coating and in many cases leads to a break in the web.

The invention is based on the object of an improved method for covering film webs to create from cellulose hydrate with aqueous dispersions, in which the above-mentioned difficulties be avoided.

Process for the continuous coating of film webs made of cellulose hydrate

Applicant:

E. I. du Pont de Nemours and Company,

Wilmington, Del. (V. St. A.)

Representative:

Dr.-Ing. W. Abitz, patent attorney,

8000 Munich 27, Pienzenauer Str. 28

Named as inventor:

John Warren Meier, Madison, Tenn. (V. St. A.)

Claimed priority:

V. St. v. America October 2, 1958 (764 889)

The method according to the invention for solving this problem is characterized in that at least ten smoothing rollers are used which rotate at a peripheral speed of 65 to 85% of the web speed.
In general, the coatings produced in accordance with

Invention can be applied, coatings of the type that are most desirable in the packaging sector are, like coatings with targeted water vapor and gas permeability, heat-sealing and not heat-sealing coatings, e.g. B. coatings

Coating compositions according to U.S. Patents 2,819,984.2,805,963,2748027,2744080 and 2,570478. The present invention reveals the critical factors - namely, peripheral speed and number of smoothing rollers - to be streak-free after the roller coating process Product.

The critical values specified according to the invention are not suggested by the prior art, rather, known processes (U.S. patent

Documents 1,776,398 and 2,388,339) for covering paper webs straight from those according to the invention critical values, as these only apply to the counter-rotating smoothing rollers a higher speed is required than for the material web.

The method according to the invention is described below with reference to the drawings, which are shown in schematic form Representation shows a typical embodiment of an apparatus for carrying out the invention.

The film web to be treated runs under constant tension and at a constant speed exceeding 91.4 m / min into the immersion tank 2,

809 507/551

which contains an aqueous dispersion of polymers. stronger inhibitory force, necessarily on one

The foil is kept from the dipstick 3 in the bath and must be kept to a minimum. Stronger touch

The same led out and runs from the bath through the level of the smoothing rollers, however, obviously

the gap of a set of squeegee rollers 4, 5, which have little effect on the formation of streaks, such a distance from one another that on both 5 The diameter of the smoothing rollers is even

Surfaces of the film a dispersion coating if contributes to the strength of the streaking in the film.

predetermined thickness is obtained. Immediately after Small Rollers, an improvement (reduction

Leaving the doctor rollers and with still wet fermentation) to give the degree of streaking; the

In the state of the coating, the coated film roll diameter should therefore not exceed the vertical value step through a series of rotating smoothing io to achieve the stiffness level

rollers 6 out, which is inevitably required in the opposite direction to the one to prevent hitting

Direction of movement of the film with a circumferential deflection or deflection of the roller at the desired

speed, the 65 to 85 ° / _{0 of} the number of revolutions is necessary.

linear speed of movement of the film. The greater the number of smoothing rollers, the more The smoothing rollers are alternately with formation 15 more effective is their smoothing effect and dement-

One set of rollers is arranged on each side of the film, mainly based on the film quality

each set consisting of at least five reels. the strength of the banding is determined. One to

The contact between the film and the rollers is a small number of rollers ineffective, and too large

takes place essentially tangentially in such a way that only one number of rollers penetrates in the manner described above minimal inhibiting force on the film to act ao in the more viscous areas of the coating, generated

comes. After passing the smoothing roller row, excessive inhibiting forces and easily leads to warping

the foil is with (not shown) conventional or tearing of the foil. In order to achieve an acceptable

dried union means to remove the water to achieve the streaking strength

and to solidify the coating or at least ten alternately arranged rollers harden. 25 can be used; twelve to sixteen reels seem

The circumferential speed and the sense of rotation to result in an optimal behavior. With increasing

with which the smoothing rollers are operated, the number of rollers can be that much faster

make for the achievement of the desired streak use, in relation to time

Formation-free coated surface critical factor and distance available for the coating process The rollers must be in opposite directions to the load.

direction of travel of the coated web with a solids or polymer content of the aqueous

Peripheral speed in the range of 65 to 85 ° / ₀ dispersion varies in the present invention

the linear speed of movement of the film as a function of the nature and the water content

are driven. At roller speeds of the hydrophilic base film to be coated, the below 65% of the film speed has the same thickness and the desired coating thickness.

Film has such a bad loading due to streaking. However, the solids content also influences the viscosity

creation that it is unacceptable. A scope that is related to stalling at high

speed of over 85 ° / _{0 of} the film speed is an important property,

speed approaches the critical speed at The viscosity should not exceed 25 cP and

which the gap between the smoothing rolls and 40 preferably fall in the range of 5 to 10 cP,

the film wiped free of flowable coating agent. The solids content of the aqueous dispersion can

and the high inhibitory levels occurring range from 17 to 65%. A salary in the range of

force leads to tearing of the film. It was found 25 to 50 ° / ₀ generally gives the best results,

that the optimal value of the peripheral speed for the total thickness of the finished dry surface

of the smoothing rollers 74 to 78% of the film speed 45 on both sides of the film, a range is preferred which

in the opposite direction, namely un- 2 ¹ I ₂ to 10 g of the dry coating per square meter

depending on the film speed, as long as this corresponds.

91.4 m / min. The following examples serve to explain

The route on which the film on or around the principle of the invention and implementation

the smoothing rollers running, or the degree of calming 50 of the invention, tion between the smoothing rollers and the film

must be steered, as too high a degree of contact Example 1

an inhibiting force which causes the film chip- _{It is an aqueous dispersion of} a mixed poly-

rmng increased, »tension folds« or »tension _{merea V (m} vinylidene chloride, methyl acrylate

"Ripples" are produced on the smoothing rollers and 55 _{md of} itaconic acid produced according to the following approach: In this way, marks are produced in the coating

g g g

in this way marks are produced in the coating.

As mentioned above, the film will tear if the inhibiting parts by weight

force becomes overpowering. It has been shown that the water 286

Degree of contact should have the size, the straight sodium lauryl sulfate (30 ° / ₀ ige aqueous

sufficient to make one touch along the entire 60 solution), »Duponok WAQ 10

Maintain roller. The film should preferably be itaconic acid 3

have a substantially tangential contact. Acrylic acid methyl ester 18

A vinylidene chloride 282 that is slightly beyond the purely tangential contact

degree of contact, about 1.6 mm, is made of ammonium persulphate 0.6 *)

For practical reasons it is desirable to use an equal 65 m-sodium bisulfate 0.3 *)

moderate film contact along all rollers safe to iron (II) ammonium sulfate 0.0075 *)

make, but has kept to this minimum _{*} The addition erfoIgt} ge _Son changed in the form of solutions are. A greater degree of contact leads to 2 to 3 parts of water (of the initial amount).

To prepare the dispersion, these components are combined in the order given a container equipped with a reflux condenser. As the polymerization proceeds, this is subject to Mixture reflux while maintaining the temperature between 32 and 36 ° C. The mixture is until the end of the rewind, which is the completeness the interpolymerization indicates, stirred. When complete implementation is used to stabilize the The following solution added to mixed polymers:

Parts by weight of sodium lauryl sulfate (3O ° / _O by weight solution)

"Duponol" WAQ 10.0

Na salt of the condensation product
from naphthalenesulfonic acid and formaldehyde, »Daxad« 11 (manufacturer die

Dewey & Almy, Inc.) 1.2

Sodium dodecyl benzene sulfonate (75 ⁰ / _o sodium
Solution), "Santomerse" 3 from Monsanto Chemical Co 8.0

Water (dissolution) 12.5

Hydrogen peroxide (30% solution) 2.5
Ethylene glycol 168.0

The resulting dispersion is cooled and discharged through a filter. It contains 39.5 ° / ₀ solids of a mixed polymer of vinylidene chloride, and itaconic acid Acrylsäurernethylester (weight ratio 94: 6: 1) and 21 ° / _o ethylene glycol and has a viscosity of 9 eP. The dispersion is applied to a film of regenerated cellulose 0.02235 mm thick by passing the film into an immersion tank containing the dispersion and then between precisely set doctor rollers in order to remove excess bath and to dose the desired amount of bath on the film. Immediately after leaving the doctor rollers, the still wet coated film is passed vertically through a series of smoothing rollers formed by twelve polished rollers 5.1 cm in diameter, half of which are alternately arranged on the two sides of the film tangential to the film. The rollers are driven in the opposite direction to the direction of movement of the film at a peripheral speed of 76% of the film speed. The film is then passed through a vertical dryer to remove excess moisture and then wound into a roll. 6 g of polymer (dry) per square meter are applied to the film, which moves at a speed of 137.2 m / min.

The coated film is transparent and has a satisfactory texture.

Example 2

The procedure of Example 1 is repeated with the exception that there are no smoothing rollers is used and the film is fed directly into the dryer after it leaves the squeegee rollers. It will a film of insufficient quality is obtained, the strong »burrs« (streaking) in the coating which extend in the machine direction.

Example3

The procedure of Example 1 is repeated except that the rotational speed is used the smoothing rollers changed; at each speed samples of the coated Slide taken. Results:

Surface speed Banding * Vpt * QTl ptl the smoothing valuation roll,% of the foil speed 4th a 60 3 b 65 2V ₂ C. 70 2 d 75 2V ₂ e 80 3 f 85 Foil tears through G 93 too high voltage

The streaking assessment is a comparative measure for the streaks or streaks that appear in the Coating appear as a series of parallel lines. The stripes are created by means of a between the Foil and a screen arranged concentrated arc lamp of the type Sylvania C 25 / DC / 5 projects the screen. In this way, the samples are rated by comparison as follows:

1 = no banding, excellent texture,

2 = slight banding,

good condition,

3 = moderate banding,

Border texture, 4 - Unacceptable streaking.

The speed of the smoothing roller is therefore optimally 75% of the film speed.

Example4

The procedure of Example 1 is repeated except that the number of smoothing rolls is changed. Results:

40 attempt Number of rollers Banding
valuation a 6th 4th b 10 3 45 C. 12th 2 d 16 1V ₂

The optimum number of smoothing rollers at a coating speed of 137.2 m / min is twelve, because despite the superior smoothing by means of 16 rollers, the excessive film tension through The appearance of wrinkles and excessive breaks makes working with this number of rollers undesirable. The 16 rollers reach through advanced water penetration into the more viscous area of the bath.

Example 5

Example 4 is repeated with the exception that the coating speed is set to 182.9 m / min. elevated.

attempt Number of reels Banding
valuation a
b
C.
d 6th
10
12th
16 4th
3
2
IV ₂

Solids content
of the bathroom viscosity
cP Banding
valuation 39.5
37.0
35.5 9
7V ₂
6th 2
l ^3/4
i ^x / ₂

Example 7

At a higher film speed, 16 smoothing rollers work completely satisfactorily, as one longer distance is available behind the squeegee rollers for smoothing. You can use a slide accordingly with superior consistency at higher speeds.

Example 6

Example 1 is repeated with the exception that the solids content of the dispersion is increased by addition the amount of water required in each case for the bath initially produced varies. The following Table illustrates the degree of smoothness improved with a lower viscosity bath is obtained.

Coating weight
g / m ²

Example 8

The procedure of Example 1 is repeated except that the coating weight is varied. Results:

4th
5
6th

Banding assessment

2V ₂
2

IV,

1V4

25th

The procedure of Example 1 is repeated except that the smoothing rollers are over the Tangent point are also pressed into the vertically moving film and thus its degree of contact is increased. The smoothing remains relatively unaffected, but the operation of the tower is through increased inhibiting forces, which lead to wrinkles and warps and more frequent tearing.

35 Lower coating agent applications lead to a reduction in the distance available for smoothing above the doctor rollers, since the reduced amount of the aqueous phase is absorbed more quickly by the base film will. The smoothness is accordingly worse, the lower the amount of coating applied.

The present invention enables banding to be reduced to one for commercial use acceptable value while allowing efficient production.

Claims (1)

Claim: Process for the continuous coating of film webs made of cellulose hydrate with aqueous dispersions of polymers, in particular vinylidene chloride copolymers, in which the coated surfaces come into contact with smoothing rollers which are arranged on each side of the web and move in opposite directions to the direction of movement of the web, characterized in that with at least ten smoothing rollers are worked, which rotate at a peripheral speed of 65 to 85 ° / _{0 of} the web speed. Considered publications:
VDI.-Zeitschrift, 1958, p. 547. 1 sheet of drawings 809 507/551 1.68 © Bundesdruckerei Berlin